I. Field of the Invention
The invention pertains to aqueous machining fluid admixtures employed in the shaping and working of metal and solid non-metallic workpieces and to processes using the machining fluid admixture. Additionally the invention pertains to aqueous machining fluid admixtures containing sulfurized oil and dimercaptothiadiazole salt components which exhibit improved machining performance.
Machining operations mechanically work and shape metallic and solid non-metallic workpieces by cutting and non-cutting operations. The cutting processes include, for example, grinding, turning, drilling, milling, tapping and broaching. Non-cutting processes may include, for example, rolling, drawing, extruding, drawing and ironing, punching, stamping and spinning.
Machining fluids are generally broadly classified into two categories, namely oils, or "straight" oils (i.e. non-aqueous fluids) which are based on oils, and aqueous fluids which are based on water. Both categories commonly include one or more additives, such as, for example, extreme pressure agents which maintain lubricating properties even when subjected to extreme pressure, corrosion inhibitors which reduce or prevent corrosion of tools, workpieces and other items contacted by the fluids, bactericides and/or fungicides which reduce or prevent microbial attack of fluid constituents, and odor control agents.
Aqueous based machining fluids comprise complex combinations of water, lubricant, surfactants, foam control agents, and additives according to the intended application. The surfactants are used to form stable suspensions of water insoluble components in the aqueous fluid base and the foam control agents reduce or prevent the generation of foam. Aqueous based fluids are far less flammable than oils, are typically more readily disposed of and less costly. However, aqueous based fluids can be less effective at reducing friction than oil based fluids and hence perform less favorably as reflected in such measures as cutting force or grinding ratio (G-ratio), i.e. in grinding operations the ratio of metal removed to volume of wheel consumed in machining.
II. Description of Related Art
Many oil based machining fluids employ sulfurized oils to achieve effective friction reduction in machining operations. These sulfurized oils often have a high sulfur content which contributes to generation of undesired odors and fumes from heat generated in a machining process. To overcome relative performance deficiencies of aqueous fluids, it has been known to employ sulfonated oil and/or sulfurized oils as lubricants, especially in fluids for grinding operations. For example, use of sulfurized oils in aqueous based fluids is known from U.S. Pat. Nos. 5,391,310, 5,368,758, 5,318,712, 4,978,465, and 3,027,324. Generally, the improved cooling properties of aqueous fluids reduces or eliminates the contribution of sulfurized oils to odors and fumes from process generated heat. Nevertheless, even aqueous fluids containing sulfonated and/or sulfurized oils have not achieved sufficient performance improvement to replace oil based machining fluids in all applications. Hence, there is a continuing need to improve performance of aqueous based machining fluids.